The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present technology.
Secondary growth of fungi in cereal grains is a common post-harvest issue arising when (pre-infected) crops become infested with fungi during storage or food processing. A notable example of the problems associated with secondary fungal growth is that of barley, commonly used in malting and brewing. A variety of species of Fusarium fungi may contaminate harvested barley if the barley was grown during a wet summer or if the barley was improperly stored (e.g., in a humid environment). Certain species of Fusarium are highly pathogenic to humans and may produce potent mycotoxins, some of which are carcinogenic.
Certain steps in the malting process for barley and other cereal grains can exacerbate fungal or other microorganism contamination. The malting process for cereal grains can be viewed as including four major steps: cleaning and sizing of the grains, steeping, germination, and kilning. Cleaning and sizing is performed to remove contaminated or damaged kernels and other undesirable materials. Steeping involves submersing the cleaned grain in cool-to-warm water, such that the moisture content of the cleaned grained is increased. The bottoms of steeping tanks may be fitted with equipment to facilitate agitation, aeration and washing of the cereal grain during steeping. The final moisture level of the steeped cereal grain will vary depending on the intended use of the malt, however, moisture levels in the range of 35-50% are common for steeped cereal grains such as steeped barley. A cereal grain may be subjected to more than one steeping, employing resting or aeration steps between steepings.
The steeped cereal grain is transferred to germination bins (or floors), and temperature- and humidity-controlled air is passed through the steeped cereal grain, which may be periodically mixed or turned. Alternatively, the steeped cereal grain may be sprayed with water to maintain the proper humidity. The temperature and humidity levels of the air vary depending on the desired qualities of the final malt, but temperatures of 12-25° C. and a humidity level approaching 100% are commonly employed. During the germination period (typically 2-7 days), the seedlings metabolic systems become fully activated, as evidenced by the emergence of rootlets, growth of the acrospires (coleoptile, spire, blade) and large increases in respiration and heat output. The germination period serves to develop enzymes required to modify the cereal grain's starches into sugars such as glucose, fructose, sucrose, and maltose.
After germination, the “green malt” is transferred to a kiln and dried using warm air (e.g., 40-60° C.) such as to reduce the moisture content of the malt (typically to approximately 20%), thereby arresting further germination. Malt used in brewing may be further subjected to further kilning (curing) at elevated temperatures (e.g., 60-105° C.), thereby reducing the moisture content to approximately 3-6%. Typically, kilning may last for 12-24 hours, although longer periods may be used.
In malting, the steeping and germination processes create ideal environmental conditions (i.e., warm and moist) under which various Fusarium species and other pathogens may flourish. Thus, such pathogens may be concentrated in the final malt or products derived therefrom, such as beer. Moreover, some toxins produced by pathogens are heat stable, and survive the kilning process. For example, certain potent mycotoxins produced by Fusarium such as deoxynivalenol, HT-2, and T-2 are largely unaffected by the kilning process and eventually make their way into beer produced from Fusarium-contaminated cereal grains. In addition to food safety concerns, microorganism contamination in malted cereal grains is also associated with a variety of quality issues in food and beverages derived from such cereal grains. For example, certain metabolites and enzymes produced by Fusarium in contaminated barley are associated with off-flavors in malt, wort, and beer. Such metabolites and enzymes produced by Fusarium and other microorganisms found on barley and other cereals, may also contribute to the undesired phenomenon known as beer-gushing. In beer gushing, beer spontaneously, without agitation, vigorously over-foams out from its packaging immediately on opening.
There is significant interest in developing effective decontamination methods for cereal grains used in malting processes. Ideally, such decontamination methods reduce or eliminate microorganisms and their associated toxins and metabolites. Further, such decontamination methods should help reduce beer gushing caused by some microorganisms. However, such methods should not impact the quality of the final malt or products produced therefrom.